Conventionally, image processing apparatuses such as display devices, imaging devices, image coding apparatuses, and image decoding apparatuses process images in units of a pixel. Each pixel includes three individual sub-pixels of green, red, and blue (RGB). A display device mixes colors of pixels by controlling the intensity of each sub-pixel. The number of intensity levels is varied for each sub-pixel. This variation in the number of levels depends on the bit depth of each sub-pixel color.
A bit depth indicates information capacity per pixel, and specifically indicates the number of bits per sub-pixel. For example, a pixel with an 8-bit depth enables representation at 256 (2 to the 8th power) intensity levels for each of its sub-pixels. As another example, a pixel with a 10-bit depth enables representation at 1024 (2 to the 10th power) intensity levels for each of its sub-pixels.
The number of combinations of intensity levels for the three sub-pixels in each pixel with an 8-bit depth is 256 to the 3rd power (16,777,216). Whereas the number of combinations of intensity levels for the three sub-pixels in each pixel with a 10-bit depth is 1024 to the 3rd power (1,073,741,824). Accordingly, the number of colors reproducible using pixels with a 10-bit depth is 64 times higher than the number of colors reproducible using pixels having an 8-bit depth.
Recently, display devices for professional use can represent images having a 12-bit depth or a 16-bit depth. Some of display devices for consumer use can represent images having a more than 8-bit depth.
Display devices capable of reproducing a greater number of colors can provide smoother transitions from color to color and a more realistic representation of real-life colors. Stated differently, a deeper bit depth yields smoother transitions from color to color and a more realistic representation of real-life colors. For this reason, consumers would prefer images having a 10-bit depth to images having an 8-bit depth as images to be represented. Methods of representing images having a greater bit depth include a method disclosed in Patent Literature (PTL) 1.
An image represented with an 8-bit depth is called an 8-bit image. Likewise, an image represented with a 10-bit depth is called a 10-bit image.